This invention relates to wheeled vehicle suspensions, and more particularly to tandem axle suspensions, which are also referred to as bogies.
The invention is especially concerned with tandem axle suspensions for trailers, involving a suspension of the type referred to as a walking beam suspension, generally comprising a pair of so-called walking beams, one for the right side and the other for the left side of the trailer, and a pair of axles, one constituting a forward axle and the other a rearward axle. Generally, prior walking beam suspensions have been subject to high stresses in the walking beams and have required the use of relatively massive and relatively expensive center pivot joints. While prior spring suspensions of the leaf spring type are not subject to these problems, other problems may be encountered in their use, such as hard riding, brake hop, instability and loss of control during braking, cornering and lane changing. With prior leaf spring suspensions, brake hop may occur when, on application of the vehicle's brakes, a condition called spring wind-up occurs which results in the tires breaking traction or sliding, the springs releasing their energy, the cycle of wind-up, traction breaking or sliding and spring energy release being repeated over and over. Instability results generally from the free play in the suspension, which is the distance or clearance between the bottom of the springs and the bolts which hold the suspension from falling out if the vehicle is lifted. In a typical trailer, the free play may be approximately two inches, which is of such magnitude as to create a tendency for the trailer to turn over. Prior leaf spring suspensions have not been wholly successful in economically obtaining equal axle loading to reduce road shock, and have also involved problems in carrying out adjustment of axle alignment.